Front glass called touch window glass for implementing the touch function of a liquid crystal panel is mounted on a portable terminal, such as a smart phone. Such front glass conventionally has a plan shape, but a product having a 3D shape in which at least one side has a curved surface is recently released.
FIG. 1 shows an example of touch window glass having such a 3D shape. The illustrated touch window glass includes a plane area A, that is, a central part and curved surface areas B formed to have curved surfaces on both sides of the plane area A. Furthermore, another example includes touch window glass in which a curved surface area is formed only on one side with respect to the plane area A, that is, a central part. Yet another embodiment includes touch window glass in which all of four sides generally surrounding the plane area A, that is, a central part, are formed of curved surface. In the touch window glass in which all of the four sides are formed of the curved surfaces as described above, pressure of an upper mold that is downward directed has a direct effect on a product.
Touch window glass having at least one curved surface area as described above is called 3D glass or curved touch window glass. Furthermore, various methods are used to form such 3D glass or curved glass, and a mold is basically used in the methods. Furthermore, the most basic form is shown in FIG. 2. In the example of FIG. 2, after glass G is placed between an upper mold 10 and a lower mold 12, curved glass, such as that described above, is formed by heating and pressurization.
In this case, a mold may be formed so that the upper mold 10 and the lower mold 12 corresponding to the entire curved glass generally come into surface contact with portions that belong to the upper mold 10 and the lower mold 12 and that come into contact with the curved glass. Alternatively, a mold may be designed so that part of a portion (i.e., a plane area) that belongs to the curved glass and that forms a plane is supported so that it can maintain the plane state by coming into contact with the upper mold 10 and the lower mold 12 and comes into contact with the upper mold and the lower mold only in the curved surface area.
Furthermore, FIG. 3 illustrates an example of a conventional mold disclosed in Korean Patent No. 10-1449365 issued to the present applicant. In such a conventional mold, glass G is supported between a lower mold 20 and an upper mold 24 in such a way as to maintain the plane state. Furthermore, middle blocks 22 are interposed in edge parts between the upper mold 24 and the lower mold 20 so that the location (or height) between the upper mold 24 and the lower mold 20 is maintained.
In such a state, cores 26 are inserted into the upper mold 24 from the top to the bottom. The bottom ends 26a of the cores 26 downward press the ends of the glass G in a high temperature atmosphere, thereby forming curved glass. In such a conventional example, glass in a portion in which the upper mold 24 comes into contact with the lower mold 20 forms a plane area, and curved surface areas are formed in outside parts in which the cores 26 come into contact with the glass.
A conventional forming apparatus, such as that described above, is described below. It may be seen that curved glass is formed between an upper mold and a lower mold. In a forming apparatus using such a conventional mold, however, it is practically impossible to load mold sets in multiple stages for mass production and to transfer the stacked mold sets to a high temperature chamber.
In the example of FIG. 2, if another mold set is stacked onto the upper mold 10, formed curved glass may be adversely affected because a downward force is applied to the upper mold 10. Furthermore, in the example of FIG. 3, if another mold set is stacked onto the upper mold 24 or the cores 26, an external force from the top is applied to the upper mold 10 or 24. If an external force is applied to the upper mold 10 or 24 as described above, there is a good possibility that it may be difficult to produce high-quality curved glass because the external force is applied to glass. If it is difficult to accurately load a mold, having an external appearance different from that of the molds of FIGS. 2 and 3, in multiple stages, mass production using the multiple stages of the molds may not be thought.